/**
 * fetch a URL.
 * Apart from the first parameter, this implements the [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API).
 * (Using this method rather than another enables outputting of curl commands with `-c` and a couple of defaults suitable for pentf).
 *
 * @example
 * ```javascript
 * const response = await fetch(config, 'https://example.org/json-api', {
 *     method: 'POST',
 *     headers: {
 *         'Content-Type': 'application/json',
 *     },
 *     body: JSON.stringify({
 *         key: 'value',
 *     }),
 * });
 * assert.strictEqual(response.status, 200);
 * const data = await response.json();
 * ```
 * @param {*} config The pentf configuration object.
 * @param {string} url URL to fetch.
 * @param {RequestInit & { agent?: any, curl_include_headers?: boolean, curl_extra_options?: any, cookieJar?: any}} [init] fetch options, see [`RequestInit` in the Fetch Spec](https://fetch.spec.whatwg.org/#requestinit).
 * On top of the standard Fetch parameters, we support the following nonstandard parameters:
 * - `agent`: node [HTTP/HTTPS agent](https://nodejs.org/api/https.html#https_class_https_agent)
 * - `curl_include_headers`: boolean (default false) of whether to include `-k` in the curl output.
 * - `curl_extra_options`: List of extra options for the curl output.
 * - `cookieJar`: A [CookieJar object](https://github.com/salesforce/tough-cookie/blob/master/README.md#cookiejar) to use.
 *               Pass in the string `'create'` to create a new one (returned as `response.cookieJar`).
 *               The response will have a utility function `async getCookieValue(name)` to quickly retrieve a cookie value from the jar.
 * - `preferNativeFetch`: use native node.js fetch instead of node-fetch. (experimental, doesn't work with self-signed certificates)
 * - `timeout`: timeout in ms
 */
export function fetch(config: any, url: string, init?: (RequestInit & {
    agent?: any;
    curl_include_headers?: boolean | undefined;
    curl_extra_options?: any;
    cookieJar?: any;
}) | undefined): any;
/**
 * Modify fetch options for a request authenticated with a client-side TLS certificate.
 *
 * @example
 * ```javascript
 * const init = {method: 'POST', body: '{"something": "secret"}'};
 * await setupTLSClientAuth(init, 'key.pem', 'cert.crt');
 * const response = await fetch(config, 'https://protected.example.org/', init);
 * assert.equal(response.status, 200); // 401 = invalid certificate
 * ```
 * @param {Object} fetchOptions The fetch request option object to modify. (`init` parameter in [[fetch]] above)
 * @param {string} keyFilename Name of the private key file in PEM format (e.g. beginning with `-----BEGIN RSA PRIVATE KEY-----`)
 * @param {string} certFilename Name of the certificate file in PEM format (beginning with `-----BEGIN CERTIFICATE-----`)
 * @param {boolean} rejectUnauthorized to validate the server's certificate, false (=default) to accept invalid certificates as well.
 */
export function setupTLSClientAuth(fetchOptions: Object, keyFilename: string, certFilename: string, rejectUnauthorized?: boolean): Promise<void>;